|Japan has asked the Chinese side to take "appropriate measures to avoid escalation of the situation"
China has summoned Japan's ambassador to demand the release of a Chinese fishing boat captain detained last week, in the worst diplomatic spat between the two regional rivals in years.
Zhan Qixiong and his crew were seized following a collision on September 7 between his trawler and two Japanese coastguard vessels in disputed waters.
Japan says Zhan rammed the two Japanese coastguard patrol vessels intentionally during a high-seas chase near disputed islands in the East China Sea, which are claimed by both countries as well as Taiwan.
The maritime incident has strained ties between the two Asian nations, and China has since summoned Uichiro Niwa, the Japanese envoy, repeatedly.
Liu Zhenmin, the Chinese assistant foreign minister, called Niwa on Tuesday to complain again over Japan's continued "illegal detention" of the Chinese skipper.
In a statement posted on the ministry's website, Liu "demanded that Japan immediately release and send back the Chinese boat captain."
The trawler's 14 crew members were released on Monday.
The Kyodo news agency citing a statement from the Japanese embassy quoted Niwa as telling Liu that China should rein in actions that could worsen the row.
"We request that the Chinese side implement appropriate measures to avoid escalation of the situation," Niwa said.
He chided China for "taking unilateral action by deliberately linking the fishing ship collision case with several unrelated issues," the Kyodo report added.
Beijing has already postponed talks with Tokyo on joint energy exploration in the East China Sea and scrapped a trip to Japan by a senior legislator in protest.
Japan on Tuesday called the situation "extremely regrettable," and has complained to China over the postponement of the energy talks.
Call for dialogue
The uninhabited islands – called Senkaku in Japan and Diaoyu in China – lie in an area with rich fishing grounds that is also believed to contain oil and gas deposits. The area has been a frequent flashpoint of regional tensions.
Meanwhile the United States on Tuesday called for dialogue to settle the dispute.
"On this narrow issue, we hope that would be resolved peacefully through dialogue between China and Japan," Philip Crowley, a US state department spokesman, said in Washington.
He also stressed the importance of the US-Japan alliance.
The alliance "is a cornerstone of security and stability across Asia," Crowley said, and benefits Japan and "other countries in the region, including China".
Relations between Beijing and Tokyo have long been dogged by mutual distrust and Chinese bitterness over Japan's occupation of much of China before and during World War II.
Both sides have made a determined effort to improve ties since 2005 and 2006, when Chinese anger with Japan erupted in sometimes violent protests and the two countries' leaders were barely on speaking terms.